1. Field of the Invention
This invention relates to a process of preparing aligned, in-situ, two-phase single crystal composites of titanium-aluminum-niobium alloys having improved room temperature ductility, oxidation resistance and high temperature creep strength. More specifically, this invention relates to a process of preparing high-temperature materials made from an alloy of titanium-aluminum-niobium (Tixe2x80x94Alxe2x80x94Nb) especially useful in internal combustion engines, gas turbines, aircraft engines, and the like.
2. Description of Prior Art
Extensive research has been devoted to the development of intermetallic materials, such as titanium aluminides, for use in the manufacture of light weight structural components capable of withstanding high temperatures and stress. Alloys based on the intermetallic TiAl are candidate materials for use in high temperatures and aggressive environments, such as those encountered in many aerospace applications. The benefits of using TiAl based alloys in engine components are their high-melting points and low densities compared to other high temperature, high strength alloys. Thus, TiAl alloys offer the possibility of attractive properties at considerable savings in weight. The major problem limiting the practical use of the alloys is its poor ductility and formability at low temperatures. Attempts have been made to improve the ductility of these alloys through the addition of alloying elements such as Ta, Mn and Nb. For example, U.S. Pat. Nos. 4,842,819; 4,857,268; 4,879,092; 4,897,127; 4,902,474; and 4,916,028, describe TiAl intermetallic materials having one or more alloys to improve room temperature strength and ductility. The addition of Nb or Nb and C, is described in these patents. Specifically, U.S. Pat. No. 4,716,020 describes titanium-based intermetallic alloys containing from 24 to 27% Al, and 11 to 16% Nb.
This invention relates to the process of preparing aligned, in-situ, two-phase single crystal. alloys of titanium-aluminum-niobium (Ti43 to 45 Al-10 to 12 Nb in atomic percent) which comprises growing the two-phase single crystal alloys at rates of about 3.0 to 6.0 and preferably from about 3.5 mm. to 5.0 mm. per hour by rotating a seed rod alloy consisting essentially of Ti-43 to 45 Al-10 to 12 Nb+0.5 Si, in atomic percent, at about 7.75 to 8.5 RPM (rounds per minute) and preferably about 8.0 RPM while in contact with a rotating feed rod alloy consisting essentially of Ti-43 to 45 Al-10 to 12 Nb, in atomic percent rotating at about 5.75 to 6.5 RPM and preferably about 6.0 RPM in an atmosphere of substantially pure inert gas such as argon at melt temperatures ranging from about 1650xc2x0 C. to 1750xc2x0 C. and preferably at about 1700xc2x0 C. to 1730xc2x0 C. to obtain two-phase single crystal alloys consisting essentially of Ti-43-45 Al-10 to 12 Nb, in atomic percent. The two-phase single crystal composites of titanium-aluminum niobium are characterized as having improved ductility, excellent oxidation resistance, and high-temperature creep strength.
Accordingly, it is an object of this invention to provide a process of preparing a two-phase single crystal, in-situ, composites of titanium-aluminum-niobium alloy that has excellent oxidation resistance at high temperatures.
It is another object of this invention to provide a process of preparing two-phase single crystal alloys, in-situ, composites of Tixe2x80x94Alxe2x80x94Nb having improved room temperature ductility and high temperature creep strength.
It is a further object of this invention to provide a process of preparing alloys characterized as having high strength and acceptable ductility for use in high temperature applications.
The above and other objects of this invention will become apparent from the following description of the preferred embodiments in combination with the accompanying drawings.